Occurrence, Inactive

Commodities and mineralogy

Main commodities Cr; Ni
Ore minerals chromite; magnetite

Geographic location

Quadrangle map, 1:250,000-scale TL
Quadrangle map, 1:63,360-scale C-4
Latitude 62.692
Longitude -151.82
Nearby scientific data Find additional scientific data near this location
Location and accuracy Reed and others (1978, locality 27) show this occurrence in the northwest quarter of Section 13, T. 30 N., R. 14 W., of the Seward Meridian on a northerly tributary of the Yentna Glacier at about 3300 feet in Denali National Park and Preserve.

Geologic setting

Geologic description

Disseminated chromite in mafic and ultramafic rock cut by thin veinlets of magnetite and minor amounts of sulfides were noted by Cobb and Reed (1980) at this locality.
This is one of several chromite occurrences in a 25-mile long belt of alpine-type ultramafic bodies described by C.C. Hawley and Associates, Inc. (1978, Fig. 4.1-(C)3 and Fig. 4.0-B), as part of the Dall Trend, that are discontinuously exposed from the Dall Glacier northeast to the Lacuna Glacier. These chromite- and magnetite-bearing dunite and peridotite sills are shown by Reed and Nelson (1980) in a narrow belt of middle to upper Paleozoic sedimentary rocks that are exposed between the middle Tertiary (38 m.y.) Foraker pluton and the northwest-trending fault which places the Paleozoic rocks over the Mesozoic marine sedimentary rocks (KJs). Foley and others (1997, p. 431) suggest that these ultramafic bodies may be genetically related to the composite plutons (Tcp) of Reed and Nelson (1980) in the upper Yentna River.
Reed and others (1978) describe these occurrences as magmatic segregations of podiform and disseminated chromite hosted in dunite sills. Chromite occurs as disrupted, irregular pods of various shapes, as much as 6 feet thick and 60 feet long, and as disseminations and streaks throughout the dunite. Other chromite occurrences in this trend are described in TL 02, TL003, TL008 - 011, and TL 055.
Geologic map unit (-151.822245807557, 62.6914544090542)
Mineral deposit model Podiform chromite (Cox and Singer, 1986; model 8a).
Mineral deposit model number 8a
Age of mineralization Mesozoic and (or) Paleozoic (Reed and Nelson, 1980) or Late Cretaceous/early Tertiary (?) (Foley and others, 1997).

Production and reserves

Workings or exploration Reconnaissance mapping, stream silt and rock sampling are all that have been done here. Chromium content of 0.7 to 1% from typical dunite is given in Reed and others (1978). The average of 3 microprobe analyses of one sample was 58.4% Cr2O3, 21.1% FeO, 8.9% MgO, and 9.7% Al2O3.
Indication of production None

Additional comments

Mineral occurrences in the Dall Trend are all within Denali National Park and Preserve.